Entropy Production Research Articles

Experimental investigation of nickel-based nanofluid on the performance of evacuated tube solar collector

This paper conducts an experimental investigation of an evacuated tube solar collector type solar collector employing a unique Ni/water nanofluid to assess its exergetic and energy performance. The investigation sheds light on the intricate behavior of nanofluid and their consequential impact on the efficiency, thermal properties, and entropy generation within the framework of evacuated tube solar collector (ETSC). The study reveals that an escalation of nickel nanoparticles volumetric concentration results in a reduction of specific heat capacity, attributed in part to the clustering effect of nanoparticles mixed with working fluid. Nevertheless, higher temperatures counterintuitively lead to an augmentation in specific heat capacity. The study presents the comparative behavior of nanofluid and the parent base fluid. The study further elucidates that augmenting the volumetric concentration of nanoparticles causes a reduction in the temperature difference between the collector's both side inlet and outlet, affecting thermal efficiency positively. Moreover, with mass flow rate contribute and increased volumetric concentration to a diminished outlet temperature, thereby enhancing the efficiency of ETSC. The study also analyzed the thermophysical properties such as thermal conductivity, viscosity, and specific heat of the Ni/water nanofluid across different volumetric concentrations and temperature ranges from 25 °C to 50 °C. Furthermore, the thermal performance of the collector was evaluated at various mass flow rates ranging from 0.0085 kg/s to 0.051 kg/s. The findings revealed a maximum energy efficiency of 73.14% at a volumetric concentration of 1% and a mass flow rate of 0.041 kg/s.

Exploration of chemical reaction and activation energy role of Jeffery-Hamel Jeffery fluid flow in penetrable non-parallel channels with entropy optimization

Recent research has demonstrated that non-Newtonian fluids exhibit superior heat transfer capabilities compared to conventional fluids. However, current methods for enhancing heat transfer in non-Newtonian fluids have their limitations. This study aims to address these limitations by investigating the influence of chemical reactions and activation energy on heat transfer within convergent/divergent channels, as described by the Buongiorno model. The study highlights several key outcomes like Higher convergence angles lead to pronounced concentration variations and gradients, whereas divergent channels result in more uniform concentration profiles. The parameter reflecting kinetic energy dominance over thermal energy shows that increasing this parameter decreases fluid temperature due to energy conversion to kinetic form. Additionally, a higher value enhances solute dispersion and energy transfer, while entropy generation increases with higher values, indicating greater irreversibility and energy losses. These insights are crucial for optimizing channel design in non-Newtonian fluid applications, aiding in the control of concentration gradients, management of temperature variations, and overall improvement in efficiency. Numerical computations of the proposed model were performed using the BVP4c scheme.

Second law of thermodynamics, heat transfer, and pumping power analyses of water and ionic liquid mixture based MXene nanofluids in a shell and helical coil heat exchanger

Heat exchangers are extensively employed across diverse sectors for efficient thermal (heat)transfer between two fluids, specifically from a hot fluid to a cold fluid. Nanofluids are promising heat transfer fluids that exhibit exceptional thermal performance in heat exchangers. The present study examines the thermodynamic second law efficiency analysis of a shell and helical coil heat exchanger utilizing MXene/80:20% water+[MMIM][DMP] (mass percentage) based ionanofluids. An analytical investigation was conducted on the heat transfer coefficient, entropy generation rate, and exergy efficiency of a shell and helical coil heat exchanger, considering particle weight loadings from 0.2% to 1.0%, Reynolds numbers from 500 to 4300, and flow rates from 0.5 to 3.5 L/min. In the base fluid, at 1.0 wt.% and at a Reynolds number of 3598, the increase in heat transfer, Nusselt number, friction factor, pressure drop, effectiveness, and frictional entropy generation are 45.59%, 28.27%, 15.19%, 12.56%, 17.20%, and 16.21%, respectively. Concurrently, thermal entropy generation, and total exergy destruction were reduced by 46.23% and 20.08%, respectively. The second law (exergy) efficiency and thermal performance factor are improved by 34.04% and 1.384-times, respectively, at 1.0 wt.% and at a Reynolds number of 3598, compared to the base fluid. The data from the current study is corroborated by existing literature. New correlations were developed from the computed data points to estimate the Nusselt number and friction factor.

Investigation of hydrothermal characteristics and entropy generation in a microchannel heat sink with elliptical fins

Abstract As the integration of microelectronic devices continues to increase, thermal management issues become increasingly prominent. Microchannel heat sinks are effective for heat dissipation in high heat flux microelectronic devices. This study designs five elliptical finned microchannel heat sinks with different aspect ratios (γ) while maintaining a constant elliptical area to enhance heat transfer performance. The values of γ are 0.74, 0.86, 1, 1.17, and 1.35, respectively. Over the Reynolds number (Re) range of 293 to 740, the hydrothermal characteristics and entropy generation of the microchannels with elliptical fins (MC-EFs) are investigated through numerical simulations. The thermal enhancement mechanism of MC-EFs is analyzed via flow, temperature, and pressure fields. The optimal γ value is determined by maximizing the overall performance factor (OPF) and minimizing the augmentation entropy generation number (Ns,a). Results indicate that introducing elliptical fins in the straight microchannel (SMC) significantly improves heat dissipation. An increase in γ enhances thermal performance but also raises flow resistance. Specifically, when γ increases from 0.74 to 1.35, the Nusselt number (Nu) improves by 10.71%-25.64%, and the friction coefficient (f) increases by 30.92%-57.27%. Overall, at Re = 740, the OPF of the MC-EF with γ = 1.35 reaches a maximum of 1.285, and at Re = 597, the Ns,a for this configuration is minimized to 0.578. These findings provide valuable insights for effective thermal management in microelectronic devices.

Generalized Itô’s lemma and the stochastic thermodynamics of diffusion with resetting

Abstract Methods from the theory of stochastic processes are increasingly being used to extend classical thermodynamics to mesoscopic non-equilibrium systems. One characteristic feature of these systems is that averaging the stochastic entropy with respect to an ensemble of stochastic trajectories leads to a second law of thermodynamics that quantifies the degree of departure from thermodynamic equilibrium. A well known mechanism for maintaining a diffusing particle out of thermodynamic equilibrium is stochastic resetting. In its simplest form, the position of the particle instantaneously resets to a fixed position x 0 at a sequence of times generated from a Poisson process of constant rate r. Within the context of stochastic thermodynamics, instantaneous resetting to a single point is a unidirectional process that has no time-reversed equivalent. Hence, the average rate of entropy production calculated using the Gibbs–Shannon entropy cannot be related to the degree of time-reversal symmetry breaking. The problem of unidirectionality can be avoided by considering resetting to a random position or diffusion in an intermittent confining potential. In this paper we show how stochastic entropy production along sample paths of diffusion processes with resetting can be analyzed in terms of extensions of Itô’s formula for stochastic differential equations (SDEs) that include both continuous and discrete processes. First, we use the stochastic calculus of jump-diffusion processes to calculate the rate of stochastic entropy production for instantaneous resetting, and show how previous results are recovered upon averaging over sample trajectories. Second, we formulate single-particle diffusion in a switching potential as a hybrid SDE and develop a hybrid extension of Itô’s stochastic calculus to derive a general expression for the rate of stochastic entropy production. We illustrate the theory by considering overdamped Brownian motion in an intermittent harmonic potential. Finally, we calculate the average rate of entropy production for a population of non-interacting Brownian particles moving in a common switching potential. In particular, we show that the latter induces statistical correlations between the particles, which means that the total entropy is not given by the sum of the 1-particle entropies.

Effect of the water erosion on the non-equilibrium condensation in steam turbine cascade

In the final stage of steam turbines, droplets formed by non-equilibrium condensation continuously impact and erode the blades, leading to changes in surface roughness and leading edge erosion. This study investigates the effects of roughness changes and leading edge erosion, induced by water erosion, on non-equilibrium condensation in steam turbine cascades using numerical simulation methods. In a Moses-Stein nozzle, the mechanism of roughness influencing non-equilibrium condensation is analyzed. Subsequently, entropy generation theory is applied to assess the loss distribution caused by roughness variations in a Dykas cascade. Furthermore, flow field analysis and entropy generation theory are utilized to examine the loss distribution pattern resulting from leading edge erosion. Results show that increased roughness delays non-equilibrium condensation, reducing average outlet humidity (from 0.05351 to 0.04361 as roughness rises from 0 to 500 µm). The effect of roughness on thermodynamic entropy generation exhibits a non-linear relationship, balancing steam flow losses with mitigated phase-change-related losses at a roughness of 896 µm. Significant blade erosion (>3 mm) alters leading edge geometry, causing local flow separation and a substantial increase in airfoil losses.

Quantum Onsager relations

Abstract Using quantum information geometry, I derive quantum generalizations of the Onsager rate equations, which model the dynamics of an open system near a steady state. The generalized equations hold for a flexible definition of the forces as well as a large class of statistical divergence measures and quantum-Fisher-information metrics beyond the conventional definition of entropy production. I also derive quantum Onsager-Casimir relations for the transport tensors by proposing a general concept of time reversal and detailed balance for open quantum systems. The results establish a remarkable connection between statistical mechanics and parameter estimation theory.

Heat transfer enhancement using ternary hybrid nanofluid for cross-viscosity model with intelligent Levenberg-Marquardt neural networks approach incorporating entropy generation

Thermal heat transfer analysis of trihybrid nanofluids using an intelligent Levenberg-Marquardt neural network (ANN-LMA) approach, with a focus on entropy generation, has been conducted. The flow equations were modeled in Cartesian coordinates and simplified using dimensionless variables. Partial differential equations were converted into ordinary differential equations through appropriate similarity transformations. These ordinary differential equations were then solved using the finite element method applied to a data set evaluated from (ANN-LMA) approach. This dataset can be input into MATLAB to generate predicted solutions for flow patterns. The ANN-LMA technique was employed to evaluate the efficiency of heat transfer characteristics for nanofluids in various scenarios. Incorporating carbon nanotubes (both single-wall (SWCNT) and multi-wall (MWCNT)) along with iron oxide in water, the study demonstrates their effectiveness in enhancing heat transfer. These nanofluids have broad industrial applications, such as in coolant enhancement, cancer therapy, and solar radiation management, and show promising results. This study specifically examines the flow properties of water-based CNT cross-trihybrid nanofluids over a convectively heated surface, leveraging their unique characteristics. Improvements in heat transfer are achieved through the introduction of dissipative heat, thermal radiation, and external heat sources or sinks. The performance of the computational solver was assessed using error histograms, regression analyses, and Mean Squared Error (MSE) results. The physical significance of the designed factors is graphically depicted and discussed in detail. It was found that radiative heat increases surface heat energy through substantial accumulation, thereby enhancing heat transfer properties, while dissipative heat, due to Joule dissipation and other external sources, significantly raises the fluid temperature.

Entropy analysis of mixed convective electro-magnetohydrodynamic couple-stress hybrid nanofluid flow with variable electrical conductivity in a porous channel

The paper presents a novel study to examine the irreversibility of quadratically mixed convective electro-magnetohydrodynamic (EMHD) flow of a couple-stress hybrid nanofluid (CSHNF) with variable properties in a vertical porous channel. The channel walls are exposed to an applied electric field effect and a uniform transverse magnetic field. The hybrid nanofluid considered is an ethylene glycol (C 2 H 6 O 2) base mixed with multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles (NPs), assuming the base fluid and nanoparticles to be in a state of thermal equilibrium following the Tiwari-Das nanofluid model. The potential applications of the study can be in microfluidics to nanofluidics, particularly in developing cooling technologies, EMHD pumps, high-end microelectromechanical systems (MEMS), and lab-on-a-chip (LOC) devices used in bioengineering. A constant pressure gradient acting in the flow direction and the buoyancy effect under the quadratic Boussinesq approximation drive the flow. The governing momentum and energy equations are nondimensionalized using pertinent dimensionless parameters and solved by the semi-analytical homotopy analysis method (HAM). The entropy generation and the Bejan numbers are derived to examine the irreversibilities in the system. To investigate the rate of shear stresses and heat transfer, skin friction coefficients and Nusselt numbers on the channel walls are determined. The analysis emphasizes the influence of nanoparticle concentration and electromagnetic field on the flow dynamics, temperature distribution, and system irreversibilities in the presence of porous media. It reveals the enhancement of fluid velocity and temperature degradation for higher concentrations. In contrast, both reduce for higher magnetic and electrical strength. With the enhancement of electrical joule heating and quadratic convection, a higher entropy generation rate is attained with a low rate of heat transfer irreversibility. However, it reduces with higher nanoparticle concentration, electrical strength, porosity, and variable electrical conductivity parameters under the dominance of heat transfer irreversibility.

Convection flow of NE-phase change material-water mixture in evacuated tube solar collector manifold: Numerical analysis of MHD double-diffusive convection and exothermic reaction

This study investigates the convection flow of nano-encapsulated phase change material (NEPCM)-water mixture in an evacuated tube solar collector manifold, focusing on the effects of magnetohydrodynamic (MHD) double-diffusive convection and exothermic reaction. Computational fluid dynamics simulations using the Galerkin finite element method were employed to analyze temperature and concentration distributions, fluid flow, melting zone of PCM nanocapsules, Nusselt number, Sherwood number, entropy generation, and thermal performance. The numerical analysis considers a range of dimensionless parameters, including Rayleigh number (Ra=103−105), Lewis number (Le=0.1−10), buoyancy ratio (Nz=1−5), nanoparticle concentration (ϕ=0.01−0.035), fusion temperature (ϴf=0.1−0.9), Stefan number (Ste=0.1−0.9), Hartmann number (Ha=0−50), magnetic field inclination angle (γ=0°−90°), and Frank-Kamenetskii number (FK=0−2.5). Results show that increasing Ra enhances the average Nusselt number (Nuav) by up to 156.1 % and the average Sherwood number (Shav) by up to 104.5 %, while increasing the total entropy generation by up to 13,155 %. Increasing FK reduces Nuav by up to 42.2 % but increases Shav by up to 13.1 %. The Lewis number and buoyancy ratio significantly influence the hydrothermal performance, with Nuav exhibiting non-monotonic behavior and Shav increasing by up to 240.9 % as Le increases. The nanoparticle concentration enhances Nuav by up to 49.7 %. Interestingly, the magnetic field effects are less pronounced than in previous studies, with Ha having a minor impact on Nuav and Shav. These findings have significant implications for the design and optimization of evacuated tube solar collectors and other thermal energy storage systems, potentially leading to improved efficiency and performance in real-world applications.

3D MHD convection and entropy production in a rectangular cavity with localized heating: A study on conductive fluid dynamics

This study aims to investigate the magnetoconvection of an electrically conducting fluid within a rectangular enclosure through a comprehensive three-dimensional computational analysis. The enclosure has a hemispherical block for bottom heating and incorporates two elliptical sources with differing temperatures along its vertical sidewalls. The primary focus is to optimize heat transfer and fluid flow characteristics within this thermal system by analyzing various control parameters. The simulations were carried out with the relevant parameters of the problem, including the Rayleigh number [Formula: see text], Hartmann number [Formula: see text], the inclination of the magnetic field [Formula: see text], and the radius of the hemispherical block [Formula: see text]. Three distinct scenarios represent different positions for the localized heat sources. Among these configurations, the Middle–Middle (MM) arrangement is the most favorable, with the specific value for the radius [Formula: see text] yet to be determined. The findings highlight the effective control of heat transfer rate and irreversibility effects by manipulating the parameters [Formula: see text], [Formula: see text] and [Formula: see text]. It is demonstrated that selecting [Formula: see text] and [Formula: see text] values of [Formula: see text] and 15 allows for optimal thermal system configuration. A correlation with two variables [Formula: see text] expressing the rate of heat transfer through the cavity was established and verified. The analysis of the helicity confirms the predicted optimal case.

Thermal quench modeling of REBCO racetrack coils under either alternating current or short-circuit voltage

Abstract Racetrack coils in REBCO High-Temperature Superconductor (HTS) motors help to increase the power-over-weight ratio by raising the magnetic flux density and output power. Nevertheless, HTS motors face thermal quench due to self-heating effects when subjected to alternating or short-circuit onset DC voltage. Additionally, thermal events have been observed due to screening currents when motors operate at high frequencies. Therefore, for the safe operation of HTS motors, quench research is crucial. To accurately simulate and analyze quench events in different scenarios, it is imperative to employ fast and precise software to numerically model the electrothermal behavior in racetrack coils. Our contribution involves the development of a novel and efficient model implemented in C++ that takes screening currents into account. This model is designed to conduct coupled electromagnetic and electrothermal analyses, utilizing variational methods. Specifically, the model incorporates both Minimum Electro-Magnetic Entropy Production and the Finite Difference Method. In this article, we explore the phenomenon of temperature rise within a racetrack coil subjected to either alternating or DC voltages of magnitudes ranging from 0.1 V to 1000 V. The study encompasses conditions of adiabatic operation and heat exchange with liquid nitrogen (LN2). Among other results, we found that in moderate DC voltages like 10 V, non-uniformity in the AC loss causes highly localized quench at the central turns. Then, screening currents play a key role also for DC voltages. The developed model exhibits the potential to comprehensively and swiftly analyze the electromagnetic and electrothermal characteristics of real-world superconducting applications, including high-field rotating machines, such as motors for aviation.

An innovative quick-decision strategy for evaluating the applicability of extractive distillation process with a preconcentration column in separating high-concentration organic waste liquid

In the face of the high energy consumption challenge in separating high-concentration organic waste liquid through extractive distillation (ED), the concept of preconcentration provides a new strategic direction. Therefore, it has become crucial to determine the suitability of the ED process with a preconcentration column for processing such complex mixture. Taking this into consideration, the study proposes an innovative quick-decision method that utilizes thermodynamic analysis of ternary phase diagram to determine the ratio of theoretical product flowrate at the bottom of the preconcentration column to the feed flowrate, which serves as the basis for deciding whether to choose the ED process with a preconcentration column for handling such separation tasks. Three azeotropic systems with different thermodynamic characteristics are chosen as case studies: cyclohexane/ethyl acetate/ethanol (Case 1), ethyl acetate/ethanol/water (Case 2), and n-hexane/ethyl acetate/acetonitrile (Case 3). The task of separating the above three systems is accomplished through the application of both three-column extractive distillation configuration (TCED), and four-column extractive distillation configuration (FCED). The objective functions for multi-objective optimization of all separation configurations include the minimum total annual cost (TAC), the minimum entropy generation and the minimum CO2 emissions. The research findings indicate that when the ratio of theoretical product flowrate at the bottom of the preconcentration column to the feed flowrate is not less than 0.56, or when there is a significant concentration difference among the components in the feed stream, the FCED configuration exhibits clear advantages over the TCED configuration in terms of economic, environmental, and thermodynamic aspects.

The Influence of Structure Optimization on Vortex Suppression and Energy Dissipation in the Draft Tube of Francis Turbine

Under partial load operating conditions, vortex rope generation in the draft tube of a Francis turbine is considered one of the main reasons for hydro unit vibration. In this paper, a Francis turbine HLA551-LJ-43 in the laboratory was taken as a prototype. Numerical simulations of the entire flow passage were carried out. Four different hydro-turbines were chosen to analyze the effect of vortex suppression, which were named the prototype turbine (N-J), the turbine with J-grooves installed on its conical section (W-J), the one with extending runner cone (C), and the one that considered the J-grooves and the extending runner cone at the same time (J+C). Under the part load conditions in which the vortex rope is easily generated (0.4–0.8 times design flow QBEP), the spectrum characteristics of pressure fluctuation, the morphology of vortex rope, and the energy dissipation based on the entropy production theory in the draft tube were studied. The results show that the three optimized structures W-J, C, and J+C could reduce the pressure pulsation in the conical section of the draft tube, weaken the eccentricity of the vortex rope, and decrease the energy losses in the runner and draft tube. It is worth mentioning that the turbine with a J+C optimized structure had the most potent effect on vortex suppression and energy dissipation. Primarily when operating in deep partial load (DPL) conditions, the efficiency of the turbine with a J+C optimized structure was increased by 13.7% compared to the prototype turbine, and the main frequency amplitude of the pressure pulsation in the draft tube was reduced to 32% of the prototype.

Small-amplitude synchronization in driven Potts models

We study driven q-state Potts models with thermodynamically consistent dynamics and global coupling. For a wide range of parameters, these models exhibit a dynamical phase transition from decoherent oscillations into a synchronized phase. Starting from a general microscopic dynamics for individual oscillators, we derive the normal form of the high-dimensional Hopf bifurcation that underlies the phase transition. The normal-form equations are exact in the thermodynamic limit and close to the bifurcation. Exploiting the symmetry of the model, we solve these equations and thus uncover the intricate stable synchronization patterns of driven Potts models, characterized by a rich phase diagram. Making use of thermodynamic consistency, we show that synchronization reduces dissipation in such a way that the most stable synchronized states dissipate the least entropy. Close to the phase transition, our findings condense into a linear dissipation-stability relation that connects entropy production with phase-space contraction, a stability measure. At finite system size, our findings suggest a minimum-dissipation principle for driven Potts models that holds arbitrarily far from equilibrium. Published by the American Physical Society 2024

Rethinking Loss of Available Work and Gouy-Stodola Theorem

Abstract Exergy represents the maximum useful work possible when a system at a specific state reaches equilibrium with the environmental dead state at temperature To. Correspondingly, the exergy difference between two states is the maximum work output when the system changes from one state to the other, assuming that during the processes, the system exchanges heat reversibly with the environment. If the process involves irreversibility, the Guoy-Stodola theorem states that the exergy destruction equals the entropy generated during the process multiplied by To. The exergy concept and the Gouy-Stodola theorem are often used to optimize processes or systems, even when they are not directly connected to the environment. In the past, questions have been raised on if To is the proper temperature to use in calculating the exergy destruction. Here, we start from the first and the second laws of thermodynamics to unambiguously show that the useful energy loss (UEL) of a system or process should equal to the entropy generation multiplied by an equivalent temperature associated with the entropy rejected out of the entire system. For many engineering systems and processes, this entropy rejection temperature can be easily calculated as the ratio of the changes of the enthalpy and entropy of the fluid stream carrying the entropy out, which we call the state-change temperature. The UEL is unambiguous and independent of the environmental dead state, and it should be used for system optimization rather than the exergy destruction.

Analysis of heat generation and viscous dissipation with thermal radiation on unsteady hybrid nanofluid flow over a sphere with double-stratification: Case of modified Buongiorno's model

PurposeThis work uses entropy generation analysis to numerically analyze magnetohydrodynamics (MHD) unsteady flow, heat and mass transfer. The study considers changing viscosity, thermal radiation, viscous dissipation, mass suction, heat generation, and stratification processes in a hybrid nanofluid around a spinning sphere. A two-phase nanofluid flow model (Buongiorno model) is used to tackle the current challenge. Both the free stream velocity and the sphere's angular velocity changed over time. Design/methodology/approachThe case study's complicated partial differential equations are transformed into simpler ordinary differential equations utilizing similarity transformation. Implementing the fourth-order Runge-Kutta Fehlberg method with a shooting scheme in MATHEMATICA has allowed us to get numerical solutions for ordinary differential structures. FindingsThe many aspects of these regulated physical characteristics have been elucidated and thoroughly examined via the use of charts and tables. For increasing values of unsteadiness parameter, the velocity profiles in the x-direction grow while they decrease in the z-direction. On the other hand, the temperature profile exhibits a dual pattern, and the concentration profile decreases. As the chemical reaction parameter climbs from 0.25 to 1.0, the Sherwood number for the nanofluid rises by 6721.39% and for the hybrid nanofluid, 3818.9%. When Nr increases from 0.2 to 0.8, nanofluid Nusselt number climbs 22.5% and hybrid nanofluid's Nusselt number rises 21.9%. The Brinkmann number and nanoparticle volume percentage are strongly associated with entropy production. Entropy generation is dual for the temperature difference, magnetic, radiation, and changeable viscosity parameters. The findings are also compared to those from the existing literature and are in excellent agreement with them.

Influence of couple stress, radiation, and activation energy on MHD flow and entropy generation in Maxwell hybrid nanofluid flow over a flat plate

Countless engineering applications rely on heat and mass transportation technologies. Limitations in thermal conductivity and mass diffusivity are common in conventional fluids. Nanofluids, which are essentially base fluids with nanoparticles suspended in them, have superior thermal characteristics than base fluids without the nanoparticles. Maxwell hybrid nanofluids have the potential to improve mass and heat transport even further by combining the characteristics of two different types of nanoparticles. The magnetohydrodynamic (MHD) flow and heat transmission properties of a Maxwell hybrid nanofluid through a flat plate are investigated in this work. The novelty of this research lies in its exploration of the combined impressions of couple stress and activation energy on the flow behaviour. The equations governing the problem undergo transformation and are handled by means of the bvp4c solver. The vital discoveries disclose that the nanoparticle concentration and magnetic field strength act as opposing forces to fluid velocity. And also, it is detected that the friction coefficient rises by 2.68% as the value of volume fraction of copper nanoparticles ranges from 0 to 0.105. It is found that there is a decrement of 29.7% in the heat transmission rate when the values of Eckert number lie between 0 and 0.6. It is observed that the reaction rate and activation energy parameters play opposite roles against fluid concentration. It is discovered that the entropy generation increases with factors that enhance friction and heat dissipation (Maxwell and Brinkman parameters). The results show that the Sherwood number drops 4.4% when the activation energy parameter is set to values between 0 and 3.

Vapor Phase Electrochemistry 2: Spherical and Spheroidal Air Plasmas

Among the rare meteorological phenomena that exist are long-lived spheroidal air plasmas. Of these, lightning balls are best characterized. Closely related are earth-lights, tornadic lights and Unpredictable Flying Objects (UFOs). Early physicists took all such phenomena to be plasmas and would refer to them as electric fire or fireballs. Many physicists today do not accept that these light emitting objects are plasmas because they neglect a variety of influences that result from chemical change. Stability results mainly from entropy production as an ionized, metastable form of nitrous acid, produced at an air plasma surface, refrigerates the surface through its conversion to the stable acid. It is then oxidized to nitric acid in an aerosol form, which restricts the inflow of air to the plasma surface. This can explain the “ surface tension” of lightning balls early, as hypothesized by Stakhanov (1979). Studies of earth-lights (Teodorani, 2004) imply that these are plasma balls held together by the same forces as those providing mechanical stability to lightning balls. Studies of flame balls in space support this view. UFOs and earth-lights are structured similarly but the plasma components of UFOs can be held together by far stronger forces. Potentially, air plasmas have important technological implications since they are all powered by extracting and using chemical energy from the air. Crucially, this energy can only be extracted from air whose temperature is below 150 C. If air plasmas could be prepared artificially, they would prove invaluable in supplying ample carbon-free electrical energy.

Energy-saving mechanism and dynamic characteristics of blade angle adjustment in low head pumping system

To investigate the energy-saving mechanisms and dynamic characteristics of blade angle adjustment, this study proposes a novel research method via simulations, prototype and model testing. For stable conditions, the internal field, the external and energy characteristics of the pumping system with different blade angle are examined. The dynamic characteristics of the pumping system and the blade force characteristics during the adjustment process are also studied. The research results show that, under a certain net head, an appropriate impeller blade angle improves the flow state in the pump and conduits, decreasing the entropy production and providing suitable inlet circulation to reduce the hydraulic loss of outlet conduit, thereby improving the pumping system efficiency by 5–10 percentage points. During the adjustment process, there is an approximate 20-s delay in dynamic characteristics. Additionally, with the increase of the blade angle, the hydraulic torques for blade axis and pump shaft increase, thus increasing the blade adjustment force and shaft power. The adjusting force is found to be underestimated in the adjustment processes of decreasing the blade angle. Achievements of this paper contribute to high efficiency of pumping system and high reliability of blade adjustment devices and pump units.